ELECTRON CONFIGURATION

Electron Configuration Arrangement of electrons in an atom Ground state electron configuration Lowest energy arrangement of electrons

THREE BASIC RULES

AUFBAU PRINCIPLE The first rule shows the order in which electrons occupy orbitals. An electron occupies the lowest energy orbital that can receive it Lowest energy level is the 1s orbital The 2s orbital is the next highest in energy then the 2p orbitals

AUFBAU PRINCIPLE (CONT’D) Beginning with the third level the energy of the sublevels in different main energy levels begin to overlap The 4p orbitals will begin to fill after the 3d orbitals are fully occupied

PAULI EXCLUSION PRINCIPLE No two electrons in the same atoms can have the same set of quantum numbers The two values of the spin quantum numbers allow two electrons of opposite spins to occupy the orbital

HUNDI’S RULE Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron and all electrons in singly occupied orbitals must have the same spin

A CLOSER LOOK AT ELECTRONS: WHERE ARE THEY IN THE ATOM?

Electrons are located within energy levels, which range from 1 to 7 Electrons are located within energy levels, which range from 1 to 7. The higher the energy the electron is in..... 1. The farther the electron is from the nucleus 2. the more energy the electron has

SUBLEVELS In each energy level, differ from each other by slight differences in energy. ORBITAL “Paths” in each sublevel that an electron can travel on

Each orbital can hold a maximum of “2” electrons. In every “s sublevel”, there is 1 orbital, which holds a total of 2 electrons In every “p sublevel”, there are 3 orbitals, which holds a total of 6 electrons In every “d sublevel”, there are 5 orbitals, which holds a total of 10 electrons In every f sublevel, there are 7 orbitals, which hold a total of 14 electrons

In what order do orbitals fill up? Low energy orbitals first, then higher energy orbitals

WRITING THE ELECTRON CONFIGURATION FOR AN ATOM

The format for the electron configuration is, for example 1 = the energy level S = the sublevel, or orbital 2 = the number of electrons in that sublevel

HOW TO WRITE AN ELECTRON CONFIGURATION

Locate the element on the periodic table Fill the orbitals in the proper order Check that the total number of electrons you have equals the atomic number for that element. Examples: Write the electron configurations for ....

Carbon Lithium Sodium Chlorine Potassium Iron 1s2, 2s2, 2p2 1s2, 2s1 1s2, 2s2, 2p6, 3s2, 3p5 Potassium 1s2, 2s2, 2p6, 3s2, 3p6, 4s1 Iron 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d6

Using Shorthand Notation for the Electron Configuration Put the noble gas that precedes the element in brackets, then continue filling the rest of the orbitals in order as usual. Examples: Sodium Potassium [Ne] 3s1 [Ar] 4s1 Chlorine Iron [Ne] 3s2, 3p5 [Ar] 4s2, 3d6

The Significance of the Electron Configurations

What is the maximum number of valence electrons an atom can have? Valence Shell The outermost energy level of an atom Valence electrons Electrons in the valence (outer) shell; important because in chemical bonding What is the maximum number of valence electrons an atom can have? 8 How do each of the noble gases differ from other atoms? They have a full valence (outer) shell

How do noble gases behave? They are not very reactive (once an atom has a full outer shell, it will not attempt to gain/lose any more electrons)